Seems to me that it would at least be worth a shot. The rear motor mount can be removed with the engine & tunnel still in place, by unbolting the crossmember from the frame and lifting the gearbox enough to slide the crossmember out. Seems to me that you could probably undo the driveshaft at the rear axle, then slide the engine and gearbox forward with the driveshaft still attached, enough to get access to the bolts that hold the driveshaft to the gearbox. Of course, you'll have to support it well enough to be safe working underneath.
(Actually, I know I've dropped the driveshaft without removing the engine or tunnel; but it was so long ago that I don't recall the details.)